1. Field of the Invention
The present invention relates to the field of earth boring tools and in particular to core catchers used for retaining cores cut during coring operations.
2. Description of the Prior Art
Coring is common practice in the field of petroleum exploration and it involves a practice wherein a drill string comprised of sections of outer tube, which ultimately terminate in a coring bit, cut a cylindrical shaped core segment from the rock formation which is then cut or broken off and brought to the surface for examination. However, it is not uncommon to encounter formations which are unconsolidated, fragmented or loose. Therefore the core, after being cut, generally will not retain a rigid configuration but must be held and retained within an inner tube which is concentrically disposed within the outer tube of the drill string. Furthermore, not only must a core catcher be activated to cut and break the lower portion of the cut core from the underlying rock formation from which it was cut, but in many cases the rock formation is so unconsolidated as in the case of oil-sand, water-sand, or loose debris, that a full closure core catcher must be used to positively seal the bottom of the inner tube if the core material is to be retained within the inner tube as the drill string is lifted from the bore hole. Such core catcher enclosures are thus manipulatively operated from the surface at the end of the coring operation and prior to retrieval of the core sample. It thus becomes desirable to have some type of means within the drill string for performing these operations and others which may become necessary during coring operations or generally within drilling operations.
Therefore, what is needed is an apparatus for manipulating or lifting the inner tube within a drill string to effect retaining of the cored material during coring operations. The apparatus must be rugged, simple in operation, reliable within the drilling environment and, preferably, automatically perform its operation once selectively initiated by the platform operator.